In the west, we have thermos flasks.
In cold climates we carry around a small to medium sized thermos flask, usually
filled
with coffee or tea when we go camping, fishing, occasionally to the park,
school.

In Beijing, thermos flasks are mainly
used for storing water .. large quantities of boiling hot water, usually so that a
whole office or classroom can make tea throughout the day.

Instead of boiling a small jug of water
in a kettle. Beijing residents often travel to a central hot water boiling
facility where they can fill up their
"giant" flasks with scalding hot water for
a tiny sum of money.

As a result, you often see people
wandering around carrying huge flasks. As usual... this is a Beijing sight
and mostly bizarre to the western tourist eye.